Conventionally, to draw a design such as a picture or a character on the surface of a solid chocolate, there is no other choice but to represent the design by hand, using chocolate of a different color or the like. A typical method first developed as a complementary technique therefor, and widely used, is a method using a mold. This mold method is for filling a mold, the surface of which has convex and concave portions thereon, with molten chocolate or the like and to allow the chocolate to set, thereby representing a picture or a character on the surface of the chocolate. The mold method, however, has the disadvantages that the method can be used only for high-volume production since it is necessary to form the mold in advance; that there are natural limits to the representation of fine lines and characters; and that it is difficult to read the picture or the character since there is no difference in the luster of the surface between the picture or character portion and the other portions.
In recent years, another widely used method directly prints a color on a chocolate by a printing process using edible ink. However, it is necessary to use another material besides the chocolate and it is also necessary to produce a transfer sheet in advance and the like. Thus this method is not suitable for high-mix low-volume production either.
In response, as a method of making a pattern appear on the surface of a chocolate cake, Japanese Laid-Open Patent Publication No. 1-141552 discloses a method of making a colored pattern appear by selectively heating the surface of a chocolate and thus by causing fat bloom. Since fat bloom, however, is caused by the crystals of fat spontaneously developing and coarsening over time, it is impossible to control fat bloom to be caused in a regular state, and thus the method cannot be used as a manufacturing method. Further, the method has a fatal disadvantage that in practice, the clarity of a picture or a character is lost when the crystals coarsen, and consequently the commercial value is reduced.
On the other hand, Japanese Laid-Open Patent Publication No. 1-108940 discloses a method of causing the focused beam of a laser light or the like to selectively irradiate and heat the surface of a thermoplastic food, and thus deforming the food by softening it or thus processing the food by performing mechanical deformation on this softened portion. In this method, however, the shapes of a picture or a character become unclear due to surface tension if several different operations are not performed instantaneously and continuously. Such operations, however, are virtually impossible in industry.
In addition, Japanese Laid-Open Patent Publication No. 2002-113585 discloses a method of: causing a laser light to irradiate a food on the surface of which an edible powder layer or a thin film layer made of an edible material having a lower melting point than the base is formed in advance; removing the powder layer or attaching the powder layer to the base, or melting the thin film layer; and thus forming a pattern by the difference in color from base chocolate. This method is widely used for industrial materials such as plastic, but when applied in practice to a chocolate, its operation process is complicated and it is difficult to even form the thin film layer on the chocolate with extremely high accuracy. Further, to completely remove the thin film layer, it is necessary to irradiate the thin film layer with extremely high laser energy, and consequently the food becomes scorched and bitter, and therefore has no commercial value as a food. Thus the method is unsuitable for practical use.
Further, when the surface of a chocolate is irradiated by a laser, the irradiated portion transpires and becomes concave. However, it is difficult to visually identify a design drawn merely by forming the concave portion on the surface of the chocolate. Particularly, a design drawn on the surface of a white chocolate is hardly visible, and unlike other common materials, a drawing cannot be easily viewable on a white chocolate merely by being engraved by laser irradiation.
Therefore, none of these conventional methods of making a drawing on a chocolate provides a method that is easy and suitable for low-volume production, without using any other materials and without impairing the taste or the flavor.